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Two hostages killed in U.S. terror strike

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(CNN)A U.S. counterterrorism operation targeting an al Qaeda compound three months ago ended tragically when two hostages, including an American held captive since 2011, were accidentally killed.

Additionally, two Americans -- both al Qaeda operatives -- were killed in U.S. counterterrorism operations in the same region, the White House disclosed Thursday.

One of the hostages killed was Warren Weinstein, an American held by al Qaeda for four years. The other, Giovanni Lo Porto, was an Italian whom al Qaeda had held since 2012.

U.S. officials had "no reason to believe either hostage was present" when the January raid was launched in the Afghanistan-Pakistan border region.

Al Qaeda leader Ahmed Farouq, an American citizen, also was killed in the operation in which the two hostages died.

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Adam Gadahn, another American who joined al Qaeda, was also killed by U.S. forces in the region "likely in a separate" counterterrorism operation, according to a White House statement.

Here are other key U.S. covert or counterterrorism operations in recent years:

Al-Shabaab leader killed -- March

Adan Garar, a member of Al-Shabaab's intelligence and security wing, was killed March 12 by a U.S. drone strike, according to the Pentagon. A key Al-Shabaab operative connected to the Westgate Mall attack in Kenya, Garar died in southwestern Somalia traveling in a vehicle.

Garar was responsible for "coordinating the terror group's external operations, which target U.S. persons and other Western interests in order to further al Qaeda's goals and objectives," the Pentagon said in a statement.

Hostages killed during Yemen raid -- December

American photojournalist Luke Somers and South African Pierre Korkie, a "respected teacher" who was to be released shortly after a U.S. Special Operations Forces raid, were fatally shot in a Yemen compound December 5 by a terrorist as the secret mission unfolded, a U.S. official said.

The element of surprise was lost in the failed U.S. military raid to rescue the two hostages being held by al Qaeda militants, a senior Defense Department official said.

President Barack Obama ordered the mission because "there were compelling reasons to believe Mr. Somers' life was in imminent danger," then-Defense Secretary Chuck Hagel said at the time.

Failed U.S. rescue attempt in Syria -- summer 2014

U.S. special operations units went into Syria in the summer of 2014 in an attempt to rescue American journalist James Foley and other hostages held by Islamic militants, a U.S. official told CNN.

In July, several dozen elite U.S. commandos from units such as Delta Force and Navy SEAL Team 6 flew in aboard helicopters but couldn't find the hostages, including Foley, whose grisly execution was captured on video and released in August by ISIS. The daring raid was carried out at an abandoned oil refinery near Raqqa, Syria.

The hostages included Kayla Mueller, a 26-year-old American humanitarian worker who was captured in August 2013. In February, her parents announced they'd received confirmation she had been killed.

Members of the Navy's SEAL Team Six targeted the foreign fighter commander for Al-Shabaab named Ikrima, a senior Obama administration official said. The SEALs came under fire and withdrew before they could confirm whether they killed their target, a senior U.S. official said.

Somalia aid workers recued -- January 2012

U.S. special forces parachuted into Somalia from fixed-wing planes, then advanced on foot to a compound holding two kidnapped international aid workers and freed them, U.S. officials said. The nine gunmen holding the hostages -- an American and a Dane -- were killed.

Jessica Buchanan, 32, and Poul Thisted, 60, had been held since October 25, 2012, when they were abducted in the central Somalia town of Galkayo after they visited humanitarian projects, according to the Danish Refugee Council, the agency for which they worked. Neither was harmed.

Killing of Anwar al-Awlaki -- September 2011

Al-Awlaki was an imam in California and Virginia before moving to Yemen.

A prominent figure with al Qaeda in the Arabian Peninsula, al-Awlaki directed an operative's failed attempt to bring down a Detroit-bound airliner on Christmas Day in 2009 as well as planned for other attacks on the United States, according to U.S. officials.

Killing of Osama bin Laden -- May 2011

In the early morning of May 2, 2011, more than 20 members of the secretive Navy SEAL Team 6 flew into Pakistan in two Black Hawk helicopters and raided a compound in Abbottabad, Pakistan.

British hostage killed in Afghanistan -- September 2010

Linda Norgrove, a British aid worker for an agency that provided various services to developing nations, was killed by her captors during a rescue attempt, officials said.

Norgrove, 36, spent much of her career managing projects for farmers and rural workers.

British Foreign Secretary William Hague said in a statement that his forces received information about where she was held and "decided that, given the danger she was facing, her best chance of safe release was to act on that information."

"Responsibility for this tragic outcome rests squarely with the hostage takers," he added.

Norgrove was being held by two Taliban commanders, Mullah Basir and Mullah Keftan, who were both killed in the raid, an Afghan intelligence official said.